Default image not appearing in WP_Customize_Media_Control

Hello,

Default image set in WP_Customize_Media_Control‘s setting isn’t appearing in the Customizer.

Here’s the code I’ve added inside in twentyseventeen_customize_register() of wp-content/themes/twentyseventeen/inc/customizer.php:

/**
 * My Test.
 */
$wp_customize->add_section(	'my-settings', array(
	'description' => __( 'Use the included default image or personalize your site by uploading your own image.<br /><br />The default images is <strong>1600 pixels wide and 1050 pixels tall</strong>.', 'twentyseventeen' ),
	'title'       => __( 'My Section Background Image', 'twentyseventeen' ),
) );

$wp_customize->add_setting(	'my-custom-image', array(
	'default'           => sprintf( '%s/assets/images/sandwich.jpg', get_template_directory_uri() ),
	'sanitize_callback' => 'absint',
) );

$wp_customize->add_control( new WP_Customize_Media_Control( $wp_customize, 'my-custom-image',array(
	'section'     => 'my-settings',
	'label'       => sprintf( __( 'My Section Image:', 'twentyseventeen' ), $image ),
) ) );

Full code: http://pastebin.com/raw/ajyXmnBY

What I expect to see:

What I see:

If I replace WP_Customize_Media_Control with WP_Customize_Image_Control, the default image appears fine.

Any idea?